Published on December 7, 2023

Side Letters: A Hidden but Influential Aspect of Contractual Relationships

In the world of contract law and business agreements, the term ‘side letter’ might not be as familiar as other legal documents, yet it plays a pivotal role in a wide array of sectors, including finance, real estate, and private equity. These documents, though ancillary to the main contract, are not mere footnotes; they carry significant legal weight and often hold the key to nuanced and specific aspects of contractual relationships.

The Nature and Function of Side Letters

Side letters are supplementary agreements that accompany a primary contract. They are tailored to address specific concerns or to grant special privileges to certain parties involved in the primary agreement. Flexibility is their main feature, providing a customization level that standard contracts often lack. For instance, in real estate transactions, a side letter might spell out specific terms for an investor, like special voting rights or a tailored exit strategy. However, these documents' confidential and exclusive nature can lead to challenges, particularly regarding transparency and fairness. This exclusivity is what sets side letters apart but also what can make them a topic of contention. They are not always disclosed to all parties involved in the main contract or other parties to the same standardized primary contract, catering instead to specific needs or arrangements with select individuals or entities.

Legal and Ethical Implications

Side Letter: Legal and Ethical Implications

Using side letters has its share of legal and ethical implications. The secretive nature of these agreements can raise concerns about fairness, especially among those not privy to the side letter. Additionally, consider when a side letter contradicts the main agreement. In that case, it can lead to complex legal disputes, necessitating careful drafting to ensure they align with the primary contract's terms and the overall legal framework or provide a framework for resolving inconsistencies between the main contract and the side letter. From a regulatory standpoint, side letters in sectors like finance often attract close scrutiny to ensure compliance with laws and to maintain equitable practices among all parties.

Side Letters in Practice

In investment funds, side letters play a crucial role by offering specific advisors and investors benefits not available to others, such as preferential fee structures or unique reporting requirements. However, fund managers must tread carefully to avoid conflicts of interest and breaches of fiduciary duties. Similarly, in real estate and private equity, these documents enable the customization of terms to individual investor needs or scenarios, such as unique management fee arrangements or specific conditions on investment opportunities. Drafting a side letter requires a nuanced understanding of legal intricacies and often involves expert legal counsel to ensure the documents are enforceable and compliant with the existing legal standards.

In the dynamic world of venture capital (VC), side letters hold a particularly strategic position. VC deals often involve multiple parties with varied interests and investment horizons, making the flexibility provided by side letters a valuable asset. These documents can be tailored to address specific investor needs, which might not be suitable for inclusion in the broader partnership or investment agreement. In VC scenarios, side letters might detail terms related to investor rights, such as preferential liquidation preferences, anti-dilution provisions, or special governance rights like board representation or veto powers on certain decisions.

Adapting to a Changing Regulatory Environment

As the regulatory environment continues to evolve, side letters are increasingly coming under the microscope. This heightened scrutiny is a response to past instances where side letters have been used to create opaque agreements that could potentially skirt legal boundaries or ethical norms. Regulators, particularly in the finance and investment sectors, are now more vigilant, seeking greater transparency and adherence to equitable practices. This shift is leading to a reevaluation of how side letters are crafted, disclosed, and integrated into the broader contractual framework.

The impact of this regulatory shift is multifaceted. For one, it demands more disclosure from parties using side letters. This transparency is not just a legal obligation but also a way to build trust among all parties involved in an agreement. It ensures that side letters do not undermine the fairness of the main contract and that their use is justified and equitable. Furthermore, this change compels legal professionals to be more meticulous in drafting side letters, ensuring that they align with the letter and the spirit of the law. This involves carefully assessing the side letter’s potential implications and consistency with the overarching regulatory framework.

Side Letter: Adapting to a Changing Regulatory Environment

This evolving regulatory landscape also influences how businesses approach contractual negotiations. There's a growing recognition that while side letters offer valuable flexibility, their use must be balanced with a commitment to transparency and ethical business practices. Companies are thus increasingly mindful of how investors, partners, and regulators might perceive their use of side letters. This awareness fosters a more conscientious approach to drafting and implementing these documents, ensuring they serve their intended purpose without raising legal or ethical concerns.

In essence, the changing regulatory environment is reshaping the role of side letters in contractual agreements. This shift is not just about compliance with laws but also about aligning business practices with evolving standards of transparency and fairness. As the business world grapples with these changes, adapting and adhering to these new standards will be crucial for maintaining the integrity and effectiveness of side letters as a tool in contractual dealings.


Side letters, though less visible than the main contracts they accompany, are indispensable in the world of complex contractual arrangements. They provide the necessary flexibility and specificity for intricate transactions but are responsible for balancing strategic needs against a backdrop of legal, ethical, and regulatory considerations. As the business and regulatory landscapes continue to evolve, the role and functionality of side letters are likely to adapt, underscoring their ongoing importance in contractual documentation. Their effective use requires legal acumen and a keen sense of fairness and ethical conduct, ensuring that these documents serve their purpose without compromising the integrity of the overarching contractual relationship.


  1. LegalVision, “What is a side letter?”
  2. Marcus, “What is the deal… with side letters?
  3. Angel List, “What is a Side Letter?”
  4. CapBase, January 3, 2023. “What is a Side Letter in Venture Capital Deals.”

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